JUST as the captain of the Rachel in “Moby-Dick” searched for his lost son and instead found Ishmael, doctors routinely reveal the unexpected while scanning for something else. What to do with this acquired information and how to follow up is becoming an increasingly vexing problem for physicians and their patients.

Unexpected finds — which the medical community has labeled “incidentalomas” — are ever more common because of an increase in scans, driven in part by legal concerns. For me, the concept of incidentalomas went from somewhat abstract to all too real when, about two years ago, an abdominal sonogram of my bladder revealed an abnormality on my pancreas. Pancreatic lesions have always had an ominous air about them because of the historically high mortality rate for pancreatic cancer, but luckily an M.R.I. and an endoscopic ultrasound confirmed the lesion as a cyst with very low malignant potential. I was advised to follow up in six months.

After I left the doctor’s office, still in that post-anesthesia state, I tried to process the phrase “low malignant potential.” I never wanted my name and the word “malignant” mentioned in the same sentence, yet “low” was certainly better than “high” and “potential” more reassuring than actual.

Still, in the next six months, I began to notice a curious new habit: checking the obituary pages to see who and how many had died of pancreatic cancer. I don’t know if I thought that someone else’s dying of pancreatic cancer would make my chances lower — as if some magical quota had been fulfilled — or higher. Regardless, I checked the section as if it were the latest political poll, stock market listing or other world event that I had precious little control over.

An increasing number of people are finding themselves in this “follow up in six months” mode, and experiencing the same attendant anxiety. The idea of waiting is in itself an existential experience. If you go online, which I often recommend that my patients do not, you find an enormous amount of conflicting information, from “must have radical surgery now” to “wait a half-year and get a follow-up scan.”

As the physicist Niels Bohr said, “prediction is very difficult, especially about the future.” But this is the exact position that many physicians and patients find themselves in. We must make life-altering decisions based on incomplete information. In my case, the decision to follow up in six months appeared to be the prudent one — and it turned out to be the right one as well. My six-month follow-up revealed the lesion unchanged. It was recommended that I follow up in another 6 to 12 months.

Welcome to the “follow-up culture.” The danger here is that we will always be living in the future: the scan was O.K., but what about in a year? No advances in medicine, as remarkable as they may be, will ever provide us solace for this predicament.

And yet, as disturbing as it is, it also provides an opportunity to live our lives to the fullest each day. As some Eastern philosophies tell us, life is like a river, in perpetual motion, and when we flow with it we attain a level of tranquillity. My patients and I will never know what the future holds for us in this new medical calendar, but my hope is that we can come to terms with the river, make friends with it, and allow it to teach us to be present in the here and now.